Vertical axis: height in meters,
horizontal axis: number of buildings with at least this height
Based on Marshall's Hot 500, july 1999.

The orange points are actual building data, the purple line is an approximation given by a simple exponential function
h(n) = h0 - h1log(n)
with
h0 = 452m and h1 = 45m
(or, if you prefer half-values
h(n) = h0 - h2·2log(n)
with
h2 = 31m.
What about the missing part, say n > 800 (or h > 150m)?
Mindless extrapolation of the purple line towards the right produces a total number of buildings in the world of approx. 22000,
which is clearly rediculous. If we reduce the average slope by a factor 4,
we end up in the region of 109, which should be about right.
For a similar graph for city skylines rather than individual buildings, see
the World's Best Skylines - analysis.